A 15 kW pump delivers 12 kgs water to a building The water c

A 1.5 kW pump delivers 1.2 kg/s water to a building. The water comes in at 100 kPa, and 15degree C. The outlet water velocity must be 30 m/s and the pump has an isentropic efficiency of 75%. How high an exit pressure can the pump produce?

Solution

Specific work Ws = 1.5/1.2 = 1.25 kW/Kg

Ideal work Wi= Ws * Effeciency

= 1.25* 0.75 = 0.9375 kW/Kg

As water is incompressible;

Wi = (Pe-Pi) v + Ve^2/2

0.9375 = (Pe - 100) * 0.001 + (30^2)/2000

Pe - 100 = (.9375 - 0.45)/0.001

Pe = 487+100

= 587 kPa... Ans